Missing a Self Assessment deadline can lead to costly penalties and interest charges, making it crucial for UK small business owners and self-employed individuals to stay on top of key dates. In 2026/27, HMRC expects timely registration, accurate submission, and prompt payment for Self Assessment to avoid fines and maintain smooth tax affairs.
Did you know that over 10 million Self Assessment tax returns were filed for the 2023/24 tax year? Staying organised well ahead of deadlines is essential to join the majority of taxpayers who meet their obligations efficiently and avoid unnecessary hassle.
| Deadline | Date | Notes |
|---|---|---|
| Register for Self Assessment (new taxpayers) | 5 October 2025 | Register with HMRC to obtain a Unique Taxpayer Reference (UTR) |
| Paper tax return filing deadline | 31 October 2025 | For 2026/27 tax year (6 April 2025 to 5 April 2026) |
| Online tax return filing deadline | 31 January 2027 | Recommended method, later but no extensions beyond this date |
| Payment deadline (balance due) | 31 January 2027 | Pay any remaining tax owed for 2026/26 |
| First payment on account | 31 January 2027 | Advance payment towards 2026/27 tax bill |
| Second payment on account | 31 July 2027 | Second advance payment for 2026/27 |
Registering for Self Assessment
Use our free Sole Trader vs Limited Company Tax Calculator to see your exact take-home pay for 2026/27. Takes 30 seconds.
Use Free Tax Calculator →If you’re new to Self Assessment, registering with HMRC is your first essential step. Registration opens after the end of the tax year in which you started trading or earned untaxed income. For the 2026/26 tax year, you must register by 5 October 2025 to avoid penalties.
Registering late means you won’t receive your Unique Taxpayer Reference (UTR) in time to file your tax return, which can lead to automatic fines. You can register online via the GOV.UK website or by calling HMRC’s Self Assessment helpline.
Filing Your Tax Return
Choosing the right method and submitting your tax return on time is critical. HMRC accepts both paper and online returns, but the deadlines differ:
- Paper returns: Must be submitted by 31 October 2025 for the 2026/27 tax year.
- Online returns: Have until 31 January 2027 to submit.
Filing online is strongly recommended. It’s quicker, provides automatic calculations, and reduces the risk of errors. You’ll need to create a Government Gateway account if you haven’t already.
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Payment Deadlines and Payments on Account
HMRC requires you to pay any tax owed by 31 January following the end of the tax year. For 2026/26, this means paying your balance due by 31 January 2027. In addition, many taxpayers must make payments on account towards the next tax year’s liability.
Payments on account are advance payments usually required if your last tax bill was over £1,000 and less than 80% of your tax was collected at source. These payments help spread your tax cost across the year.
How Payments on Account Work
Payments on account for the 2026/27 tax year are each 50% of your 2026/27 tax bill (excluding student loan repayments and capital gains tax). They are due in two instalments:
- 31 January 2027 (along with any balance due for 2026/26)
- 31 July 2027
If your income changes significantly, you can ask HMRC to reduce your payments on account.
Penalties for Late Filing and Payment
Failing to meet any Self Assessment deadlines results in penalties and interest, which escalate the longer you delay. Key HMRC penalties include:
- Late filing penalty: £100 immediately after 31 January deadline.
- Continued delay: Additional daily penalties of £10 per day after 3 months, up to £900.
- 6 months late: Further £300 or 5% of tax due (whichever is greater).
- 12 months late: Another £300 or 5% of tax due.
- Late payment interest: Charged on unpaid tax from 1 February after the deadline.
Timely registration, filing, and payment are the best ways to avoid these extra charges.
Tips to Stay on Top of Your Self Assessment
Keeping organised throughout the tax year reduces stress and ensures you meet deadlines. Here are some practical tips:
- Set reminders: Use calendars or tax apps to mark key dates.
- Keep records: Maintain accurate income and expense records year-round.
- Register early: Register for Self Assessment as soon as you start earning untaxed income.
- File online: Online filing is more flexible and offers instant confirmation.
- Pay early: If possible, pay tax early to avoid last-minute issues.
- Seek expert help: Use accountants or tax advisors if your tax affairs are complex.
For more on tax planning, see our guide on Corporation Tax and whether to operate as a Sole Trader vs Limited Company.
- Register for Self Assessment by 5 October 2026 if new to filing.
- File paper returns by 31 October 2025 or online by 31 January 2027.
- Pay your tax bill and first payment on account by 31 January 2027.
- Make the second payment on account by 31 July 2027.
- Late filing and payment penalties increase quickly, so plan ahead.
When should I register for Self Assessment if I start self-employment in 2026?
You must register with HMRC by 5 October 2025 if you start self-employment during the 2026/27 tax year to avoid penalties. Early registration ensures you receive your UTR and can file your return on time.
Can I file my 2026/26 Self Assessment return after 31 January 2027?
No, 31 January 2027 is the absolute deadline for online submissions for the 2026/27 tax year. Filing after this date results in automatic penalties and interest charges on any tax owed.
What happens if I miss my payment on account deadline?
If you miss the 31 January or 31 July 2027 payments on account, HMRC will charge interest on the overdue amount and may impose penalties. It’s best to pay on time or contact HMRC to discuss payment options.
Official Sources
* GOV.UK: Set up a business · * HMRC: Income Tax rates · * HMRC: Corporation Tax · * HMRC: VAT registration